Objectives To understand the neural system underlying the expression of emotion in primates. ABSTRACT:We have focused on elucidating mechanisms underlying the expression of fear and anxiety. This is an area of great importance because when appropriate, fear-motivation behaviors are adaptive; however, when overly intense or expressed out of context, extreme fear is characteristic of many forms of psychopathology. We are using state-of-the-art techniques to understand the role of the amygdala and its nuclei in mediating fearful states. We will assess the role of the amydala in mediating 1) classically conditioned autonomic responses, 2) ethologically relevant threatening stimuli, and 3) affiliative and defensive behavior expressed in social situations. Eventually, these studies will define biological mechanisms regulating the expression of the primate's adaptive responding to threatening stimuli. These findings will provide insight into mechanisms mediating maladaptive responding in humans, which is characteristic of fear-related psychopathology. Keywords neurobiology, amygdala, defense, behavior, brain, psychopathology, conditioning